Giant Wagon Wheel

Method

1. For the dough, put the flour and butter with a large pinch of salt in a mixing bowl. Rub with your fingers to a breadcrumb consistency. Stir in the sugar, vanilla and egg yolk with a wooden spoon. Use your hands to bring the dough together. (To make the dough in a food processor, pulse the flour and butter to a breadcrumb consistency, add the sugar, vanilla and yolk, then process to bring the dough together.)Wrap in cling film and chill for 30 minutes.
2. Heat the oven to 180°C/160°C fan/gas 4. Divide the dough in half and shape into 2 discs. Lightly dust a clean work surface with flour. Using a rolling pin, roll out a dough disc into a thick circle. As the dough starts to warm up, it will become quite sticky; place it between 2 sheets of non-stick baking paper, then continue rolling to form a large circle about 30cm diameter and roughly 0.5cm thick. Repeat with the other dough disc. Put each disc on a large baking sheet, removing only the top sheet of paper. Chill for 10 minutes in the freezer, then bake for 16-18 minutes until cooked through and just turning golden.
3. Upturn a 28cm diameter mixing bowl or plate and place lightly on top of the biscuits. Trim around using a sharp knife to form 2 neat circles. Cool on a wire rack.
4. Melt 100g of the chocolate (the dark one if using a mixture) in a heatproof bowl set over a pan of steaming (not bubbling) water; make sure the bottom of the bowl doesn’t touch the water. Spread the melted chocolate evenly over one of the biscuits, then chill in the freezer to set firmly.
5. Meanwhile, put the marshmallows in a microwavable bowl and microwave on medium power for 2-3 minutes until runny. (If you don’t have a microwave, put the marshmallows in a heatproof bowl set over a pan of simmering water and heat until melted.) Cool until the marshmallow is really sticky and spreadable but not so runny it will run off the biscuit.
6. Remove the set chocolate biscuit from the freezer and turn it, chocolate-side down, onto a board. Using a spatula, spread the melted marshmallow over the biscuit, leaving about a 1cm border. Use the back of a spoon to spread the jam on top, leaving a little marshmallow in the middle uncovered so the top biscuit will stick. Place the other biscuit on top, then chill in the freezer for 15 minutes to firm up.
7. Meanwhile, put the remaining chocolate and a knob of butter in a heatproof bowl, then set over a pan half-filled with gently simmering water. Don’t stir the chocolate, and turn the heat right down so it doesn’t seize (turn solid). Once melted, remove from the heat and cool a little so it’s not too runny.
8. Once the mallow has firmed up enough not to ooze out, take the biscuit from the freezer and put it on a wire rack with a baking tray underneath it. Pour the chocolate over and spread with a palette knife to create a smooth, thin layer, letting it dribble and ooze over the side. Keep spreading the chocolate around the edge until completely covered, letting the excess drip through the wire rack.
9. Chill the Wagon Wheel in the fridge for at least 1 hour so the chocolate firms up or until ready to serve. We like it served straight from the fridge, but you can leave it to come to room temperature if you prefer.